Journal of Environmental Engineering

This article reviews the development of our understanding of flow through porous media with a focus on understanding the clean-bed head loss in water filters. A model of the Forchheimer form is developed by typing existing empirical models to current hydrodynamic theory, and constants are developed for three filter media: glass beads, crushed silica sand, and crushed anthracite coal. Suggestions are made for future research that would improve our understanding.

The batch settling process was simulated numerically using a dynamic model for zone settling and compression. The simulation can provide the height variation of the supernatant-suspension interface with time as well as the vertical solids profile at different times. The simulation results were compared with experimental batch settling data in the literature for various types of suspended materials with different initial suspended solids concentrations. Generally good agreement between the simulations and experimental measurements was obtained. The method presented here has several advantages for the simulation of the batch settling process compared with the methods found in the literature; it is simple, requires only four parameters, and provides good results for both zone and compression settling. Also presented is a technique for quantifying all four required parameters, in particular, the two describing the compression characteristics of a suspension from batch settling tests. These compression parameters are needed to estimate the depth requirement of steady-state gravity thickeners. This method also will be useful for environmental engineering processes that use batch settling for solids-liquid separation, such as sequencing batch reactors.

An experimental method that quantifies the effect of polymer dosing on sludge settling characteristics is proposed. This method consists of recording batch settling curves at a grid of sludge and polymer concentrations. The effect of the polymer was found to depend on the mixing time between the dosing of the polymer and the start of the batch sedimentation. The recorded effects could be successfully implemented in a 1D dynamic settler model. From the literature it was concluded that keeping the sludge blanket below a certain critical height is an effective way of controlling the effluent suspended solids. From a model-based analysis this strategy appeared to be sound. Different control strategies using, respectively, the sludge blanket height [feedback (FB)], the hydraulic loading [feedforward (FF)], the solids loading (FF), or the sludge volume loading (FF) were tested for their ability to keep the sludge blanket below the critical height. The control strategy based on the hydraulic loading was the least efficient with respect to minimizing polymer dosage. The others appeared equally effective provided that they were properly tuned. Using the excess of the critical sludge blanket height as a measure of effectiveness, strategies based on more than one measured variable appeared to be less sensitive to suboptimal tuning.

A chemical mass balance (CMB) model, applied to polycyclic aromatic hydrocarbon (PAH) compounds, is used to apportion PAH sources in a group of seven sediment cores in the Milwaukee Basin of the central Lake Michigan area. PAH apportionment results indicate the dominance of coke oven emissions from 1925–1976, and of highway inputs from 1983–1992 for most of the seven cores. This is consistent with results of carbon particle analysis from the same basin. Milwaukee and Port Washington appear to be primary contributors of point source inputs of PAHs from coke ovens and highway dust. Wood burning is a minor source (<13%). These findings are supported by an independent factor analysis study. Historical PAH records are also determined for the seven sediment cores. The records are unmixed and averaged over the basin. The resulting average record is then used as measured profile in a CMB model to determine PAH sources. Source profiles are historical records of the consumption of coal, petroleum, and wood, including coal used for coke production. A cubic spline technique is developed and applied for the curve fitting of original data points for all of the cores. Unmixed profiles reveal a number of features that are not seen in the original data. Wood burning, coke oven emissions, and highway dust profiles are found to resemble the national consumption records. Coal burning is a very small PAH source (<1%).

A pilot-scale study was conducted to evaluate an integrated system for the remediation of soils contaminated primarily with pentachlorophenol (PCP), a wood preserver. The integrated soil remediation system consisted of three unit processes: (1) Soil solvent washing; (2) solvent recovery; and (3) biotreatment of the contaminant residual. Pilot-scale countercurrent solvent washing was carried out using a 95% ethanol solution—a solvent that in an earlier bench-scale study was found to be effective in removing PCP and hydrocarbons (HCs) from soils. Three-stage countercurrent solvent washing of a field-contaminated soil was performed using batches of 7.5 kg of soil and 30 L of solvent (1 kg:4 L soil-to-solvent contact ratio). The washed soil was rinsed with water in a single stage after three countercurrent wash stages. Pilot-scale, three-stage countercurrent solvent washing with 95% ethanol reduced the PCP and HC contamination on the soil by 98 and 95%, respectively. The spent solvent and the spent rinse water were combined as the spent wash fluid for further treatment. A pilot-scale distillation unit was used to recover the ethanol from the spent wash fluid. The HC constituents of the spent wash fluid were removed by pH adjustment prior to feeding the spent wash fluid to a distillation unit. Greater than 96% of the ethanol in the spent wash fluid was recovered in the distillate stream, whereas PCP was captured in the bottoms stream. The bottoms stream was treated sequentially in anaerobic and aerobic granular-activated carbon fluidized-bed reactors. Complete mineralization of PCP was achieved using this treatment train.

This paper examines the potential of using laboratory-synthesized nanoscale iron particles to transform chlorinated methanes. The iron particles have diameters on the order of 1–100 nm (0.001–0.1 μm). Palladized iron particles were prepared by depositing palladium (0.05–1% Pd by weight) on the surface of iron. Batch experiments were conducted to compare reactions of chlorinated methanes with palladized nanoscale iron, nanoscale iron, and commercial grade iron particles (∼10 μm). Rapid transformations of tetrachloromethane (CT) and trichloromethane (CF) were achieved with the palladized nanoscale iron particles. Typically 0.1 mM CT or CF was reduced below detection limits within 1 h. Methane and dichloromethane (DCM) were the major end products. Yields of methane and DCM from CT were 52% and 23%, respectively. Little degradation of DCM was observed within 72 h. With the nanoscale iron and commercial-grade iron particles, much slower reactions of chlorinated methanes were observed. Kinetic analyses indicated that the surface area-normalized rate coefficients k_SA of the nanoscale iron and commercial grade iron particles were one to two orders of magnitude lower than those of the palladized nanoscale iron.

Experiments have been conducted to investigate gas-phase adsorption characteristics of 1,1,1,2-tetrafluoroethane (HFC-134a) by activated carbon fiber, extruded activated carbon, granular activated carbon, activated alumina, and molecular sieve. HFC-134a is currently regarded as an excellent replacement for chlorofluorocarbon-12, a refrigerating and cooling agent extensively used previously in all automobiles and many cooling systems. Performances of HFC-134a adsorption were characterized by the equilibrium adsorption capacity, time to reach equilibrium, and desorption efficiency of exhausted adsorbent. A simple thermal treatment process with proper operating temperature and treatment duration was found to be effective for the regeneration of exhausted adsorbents. Adsorption isotherms of the empirical Freundlich and Jossens types were observed to adequately represent the equilibrium adsorption data. A mass transfer model based on the pseudo steady state squared driving force was adopted to describe the mass transfer process of HFC-134a adsorption.

Pilot-scale experiments were performed to investigate the effectiveness of enhanced coagulation in removing particles and trihalomethane (THM) precursors from two surface source waters: California State Project water and Colorado River water. The removal of suspended particles and natural organic matter at various ferric chloride doses and coagulation pHs was assessed through source water and filter effluent measurements of turbidity, particle count, UV₂₅₄, TOC, and THM formation potential. Overall, it was found that optimal removal of particles and THM precursors by enhanced coagulation with ferric chloride is obtained at high coagulant doses (>16 mg/L) and low pH conditions. Generally, turbidity removal is more efficient and head loss is more moderate at ambient pH compared with pH 5.5. Additionally, filter effluent particle counts were found to be consistent with residual turbidity data. The removal of THM precursors by enhanced coagulation is significantly enhanced at pH 5.5 compared with ambient pH. The reduction in THM formation potential is consistent with the trends observed for the THM precursor removal data (i.e., UV₂₅₄ and TOC data). Furthermore, specific UV absorbance was used to estimate the proportion of humic substances in the raw waters. Enhanced coagulation was found to be less effective for the source water with the lower specific UV absorbance.

Biological treatment of airstreams has been shown to be useful when the airstreams are contaminated with low concentrations of volatile organic chemicals. One type of airphase biological reactor, the bioscrubber, has operational advantages over the two other types of airphase bioreactors, biofilters, and biotrickling filters. The airlift bioscrubber is a new bioscrubber configuration that offers some advantages over the conventional two-stage bioscrubber. In this work, a practical mathematical model was developed for the airlift bioscrubber for the removal of aromatic hydrocarbons, benzene, toluene, and ethylbenzene. The model input parameters were defined, and typical values were determined from the published literature. A sensitivity analysis was conducted on the mathematical model to define the operating range of the airlift bioscrubber for the removal of the benzene, toluene, and ethylene compounds. In addition, the sensitivity analysis results were used to define the range of testing that is appropriate for laboratory validation and calibration of the proposed mathematical model.

Solid waste produced from construction and demolition (C&D) activities is typically disposed of in unlined landfills. Knowledge of C&D debris landfill leachate is limited in comparison to other types of wastes. A laboratory study was performed to examine leachate resulting from simulated rainfall infiltrating a mixed C&D waste stream consisting of common construction materials (e.g., concrete, wood, drywall). Lysimeters (leaching columns) filled with the mixed C&D waste were operated under flooded and unsaturated conditions. Leachate constituent concentrations in the leachate from specific waste components were also examined. Leachate samples were collected and analyzed for a number of conventional water quality parameters including pH, alkalinity, total organic carbon, total dissolved solids, and sulfate. In experiments with the mixed C&D waste, high concentrations of total dissolved solids (TDS) and sulfate were detected in the leachate. C&D leachates produced as a result of unsaturated conditions exhibited TDS concentrations in the range of 570–2,200 mg/L. The major contributor to the TDS was sulfate, which ranged in concentration between 280 and 930 mg/L. The concentrations of sulfate in the leachate exceeded the sulfate secondary drinking water standard of 250 mg/L. The leachate produced from lysimeters exposed to conditions of constant flooding possessed a greater concentration of dissolved constituents than leachate from the unsaturated lysimeters. The sulfate concentration ranged from 950 to 1100 mg/L. In both scenarios, the primary ions contributing to the dissolved solids were sulfate and calcium, both a result of gypsum drywall. The flooded lysimeters remained at a constant pH of 11 throughout the experiment, whereas the pH dropped to neutral conditions (pH 6–7) in the unsaturated columns after 1 month of the leaching experiment. The high pH of leachate from the flooded columns was attributed to concrete. Based on leaching tests on individual waste components, wood and cardboard were the primary materials contributing to dissolved organic carbon. The organic carbon concentrations in the leachate were generally lower than typical municipal waste leachate. The biological conversion of sulfate to sulfide was evident in many columns, and was most pronounced in the unsaturated, mixed-waste columns.

The cooling process prior to treating flue gas and the spray dryer process that removes acid components in flue gas are believed to influence the mass and elemental size distributions of heavy metal in fly ash. The main objective of this study was to investigate the effects of operating parameters on the mass and elemental size distributions of heavy metals in fly ash produced from a fluidized bed incineration and a water cooling or spray dryer flue gas treatment system. The operating parameters investigated included (1) the controlling temperature in the gas cooling system; (2) the controlling temperature in the spray dryer system; (3) the addition of organic chloride; and (4) the addition of inorganic chloride. The experimental results indicated that the water cooling process and spray dryer process increase the amount of coarse fly ash (5–125 μm) and increase the total concentration of metal in fly ash. The amounts of fine fly ash (0.1–15.72 μm) and the total concentration of metal in fine fly ash increase with decreasing temperature during the water cooling process. However, the amounts of fine fly ash (0.1–15.72 μm) and the total concentration of metal in fine fly ash decrease with decreasing temperature during the spray dryer process.